1. Field of the Invention
The present invention relates to a knitting process, employing a circular knitting machine and pile elements, for manufacturing a patterned pile fabric having different pile structures in which the pile loops can be either severed or remain uncut.
2. Description of Related Art
Pile fabrics in which a loop structure individually alternates with velour, i.e. a severed pile construction, can be produced by different methods.
In one of these methods, after knitting a plain loop fabric, the shearing machine used in a subsequent finishing process is equipped with a patterning device which, in part, avoids severing all of the pile loops. This method is limited by the requirements of the patterning device and by a single shearing action which reduces the reliability of this method.
Therefore, prior to the present invention, it has been common to knit pile fabrics having different pile lengths and to subsequently finish the longer pile loops to a velour structure by one or more shearing actions. It is obvious that the knitting as well as the finishing or shearing processes require an extraordinarily precise adjustment in order to obtain perfect velour surfaces while at the same time leaving the shorter pile loops uncut.
For knitting pile fabrics having both shorter and longer pile loops, pile elements, preferably sinkers, are provided with two different pile forming ledges and are selectively actuated between the needles by one of these ledges. Such proposals are referred to e.g. in DE-PS 656 588, U.S. Pat. No. 3,477,255 or EP-A1-0 629 727 A1.
Alternatively, forming pile loops at different lengths excludes an equalizing work step, such as stretching out, straightening and holding the pile loop during the knitting cycle of a succeeding course, at least in the succeeding feeder, for example, according to the teaching of U.S. Pat. No. 4,020,653, and is today with different variations, part of modern pile knitting methods used to avoid pile and stitch deformations leading to defects such as uncut pile loops in a velour fabric. This drawback in knitting a two-level pile fabric, and the restriction in the adjustment of the shearing machine to sever exclusively longer knitted loops, inevitably results in some defects in the velour parts of such fabrics which must be accepted.
In the past, numerous proposals for severing pile loops in the knitting machine have already been made as referred to in the introductory portion of EP-A2 0 082 538, which is incorporated herein by reference. Using this proposal, and the presence of sufficiently dimensioned pile and cutting elements that cooperate in a scissor-like arrangement, results in a satisfactory reliability in the step of severing the pile loops and in acceptable intervals for replacing worn pile and cutting elements.
The proposed methods for severing predetermined pile loops, as reported in DE-OS 1 585 051 and DE-OS 29 17 378, apparently have not been implemented under practical conditions. In these proposals it is pointed out that formation of uncut and severed pile loops, in the same course, is limited to a predetermined application of the pile elements and the adjustment of corresponding cams. Additionally, in the German patent application 1 585 051 it is noted that special fabric constructions must be knitted, for which reason the gauge of the dial is only half the gauge of the cylinder. This knitting process suffers from the disadvantage that the pile loops are cleared immediately subsequent to the stitch and pile forming process, possibly resulting in stitch and loop deformations. The clearing movement for uncut pile loops, which is identical with the severing action, is not sufficient for accurately clearing these loops when pile loops are formed by adjacent needles.